Wpf TabControl Interaction.Trigger fires mores than once - wpf

Question

I have an unexpected behaviour with a Wpf-Tabcontrol and Dataemplate with Interaction.Trgiggers.
First I define a "ViewModel". It's quite simple:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Controls;
using System.ComponentModel;
using System.Windows;
using System.Windows.Input;
namespace WpfApplication3 {
public class Vm: INotifyPropertyChanged {
public Vm() {
this.CmdClick = new RelayCommand( p => this.ExecuteClick(), p => this.CanExecuteClick() );
}
private string myName;
public string MyName {
get { return myName; }
set {
if( myName != value ) {
myName = value;
if( this.PropertyChanged != null ) {
this.PropertyChanged( this, new PropertyChangedEventArgs( "MyName" ) );
}
}
}
}
private RelayCommand cmdClick;
public RelayCommand CmdClick {
get { return cmdClick; }
set { cmdClick = value; }
}
#region Command
private bool CanExecuteClick() {
return true;
}
public void ExecuteClick() {
MessageBox.Show( "MyName is " + MyName );
}
#endregion
public event PropertyChangedEventHandler PropertyChanged;
}
}
Next, I define a Datatemplate:
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:l="clr-namespace:WpfApplication3"
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<DataTemplate DataType="{x:Type l:Vm}" x:Key="Vm">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<TextBox Text="{Binding Path=MyName}" Grid.Row="0"/>
<i:Interaction.Triggers>
<ei:KeyTrigger Key="F5" ActiveOnFocus="True" FiredOn="KeyUp" >
<i:InvokeCommandAction Command="{Binding CmdClick}" />
</ei:KeyTrigger>
</i:Interaction.Triggers>
</Grid>
</DataTemplate>
</ResourceDictionary>
I use the datatemplate on the mainform inside a TabControl:
<Window x:Class="WpfApplication3.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:l="clr-namespace:WpfApplication3"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="Dictionary1.xaml" />
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</Window.Resources>
<TabControl>
<TabItem Header="Tab1">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<ContentControl ContentTemplate="{StaticResource Vm}" x:Name="vm11" Content="{Binding}" Grid.Row="0"/>
</Grid>
</TabItem>
<TabItem Header="Tab2">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<ContentControl ContentTemplate="{StaticResource Vm}" x:Name="vm21" Content="{Binding}" Grid.Row="0"/>
<ContentControl ContentTemplate="{StaticResource Vm}" x:Name="vm22" Content="{Binding}" Grid.Row="1"/>
</Grid>
</TabItem>
</TabControl>
</Window>
The code behind is simple:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
namespace WpfApplication3 {
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window {
public MainWindow() {
InitializeComponent();
this.vm11.Content = vm1;
this.vm21.Content = vm2;
this.vm22.Content = vm3;
this.vm1.MyName = "Name1";
this.vm2.MyName = "Name2";
this.vm3.MyName = "Name3";
}
Vm vm1 = new Vm();
Vm vm2 = new Vm();
Vm vm3 = new Vm();
}
}
When i run the program, I chlick in the first TextBox, press F5 and the MessageBox posup. Ok.
I switch the tabpage, click inside the second TextBox, press F5 and the MessageBox appears again. OK.
I switch back to the firsz tabpage, press F5 and the MessageBox appears twice. Uuuh. Whatss wrong.
I switch back to the second tabpage,the messagebox appears twice again.
After switching to the first tabpage, the messagebox is displayed treetimes now. And so on.
It is like, the KeyUp-Event is assigned internaly, when the datatemplate is displayed again, without dereferencing it. But ehat can I do ?

Answer 1

I think you need to change this property from
private RelayCommand cmdClick;
public RelayCommand CmdClick {
get { return cmdClick; }
set { cmdClick = value; }
To
private RelayCommand cmdClick;
public RelayCommand CmdClick {
get { return cmdClick; }
set { if(cmdClick == null)cmdClick = value; }